This invention relates to systems for monitoring smoke density in a monitored space.
Systems for monitoring smoke density covering an extensive monitored space have been heretofore proposed and applied to detect fires and the like. A system for detecting the smoke density based on the transmittance of light radiated from a light source, allowing a comparatively large monitored space to be covered, is popular and widely used. One specific application of this system is an attenuation type smoke detector employed in, e.g., fire detecting equipment. The smoke detector is such that a light source is arranged so as to confront a light detector with a monitored space interposed therebetween so that the transmittance of light reaching the light detector from the light source is monitored and that the monitored transmittance is compared with a predetermined value to obtain a smoke detection signal.
In the case where the smoke density of the monitored space is monitored by the transmittance of light, it is advantageously that one set of devices permit monitoring an extensive space in one direction.
However, when the space to be monitored is too long, it becomes difficult to accurately detect a local rise of smoke density, and hence to locate a fire or the like. Assuming that a monitored space extending linearly from the light source to the photo detector is a collection of imaginary subspaces, only the accumulated value of the transmittances of each subspaces is obtained as a result of detection.